Light emitting diode with nanostructured layer and methods of making and using

ABSTRACT

A light emitting diode has a plurality of layers including at least two semiconductor layers. A first layer of the plurality of layers has a nanostructured surface which includes a quasi-periodic, anisotropic array of elongated ridge elements having a wave-ordered structure pattern, each ridge element having a wavelike cross-section and oriented substantially in a first direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This utility patent application is a divisional of U.S. patentapplication Ser. No. 14/172,505 filed Feb. 4, 2014 which is acontinuation of and claims priority to Russian Application No.PCT/RU2011/000594 filed Aug. 5, 2011, the benefits of which are claimedunder 35 U.S.C. §120 and 35 U.S.C. §119, respectively, both of which arefurther incorporated herein by reference.

FIELD

The invention relates to the field of semiconductor devices forconverting electrical energy into light energy, in particular to thefield of solid state light emitting diodes. The invention also relatesto the technology of forming nanostructured elements on the surface ofsemiconductor wafers to produce light emitting diodes.

BACKGROUND

In at least some arrangements, light emitting diodes (LEDs) have anactive layer of semiconductor material sandwiched between n-type andp-type semiconductor doped layers. When a voltage is applied between thedoped layers, an electric current is passed through the LED. Chargecarriers, electrons from n-layer or holes from p-layer, are injectedinto the active layer where they recombine to generate light. The lightgenerated by the active region emits in all directions and escapes theLED through all exposed surfaces (light emitting surfaces). Theefficiency of LEDs is limited by the phenomenon of total internalreflection (TIR) in which a part of the light is reflected from thelight emitting surface back into the LED and is lost due to lightabsorption. The greater the difference in refractive indices (n) of thematerials at the light emitting surface compared to the environment towhich the light exits (n=1.0 for air and for epoxy), the stronger thenegative impact of TIR. Typical semiconductor materials have arelatively high index of refraction (n≈2.2-3.8); therefore, much of thelight generated by the active layer of the LED is blocked by the lightemitting surface.

Green, blue, and ultraviolet LEDs can be manufactured, for example, withgallium nitride (GaN) epitaxially grown on substrates of sapphire(Al₂O₃), silicon carbide (SiC), silicon (Si), SiC-on-insulator (SiCOI),Si-on-insulator (SOI), or the like. Infrared, red, and yellow LEDs canbe manufactured, for example, with ternary or quaternary compounds ofA₃B₅ (Al,Ga,In)(P,As) grown on substrates of gallium arsenide (GaAs) orindium phosphide (InP). These compounds can include, in particular,aluminum containing semiconductor compounds from a group including AlAs,AlGaAs, AlGaInP, AlGaN, and AlGaInN.

The growth substrate is sometimes removed to improve the opticalcharacteristics and to reduce the resistance of LED layers. A sapphiresubstrate, for example, can be removed by laser melting of GaN at theGaN/sapphire interface, and silicon and gallium arsenide substrates canbe removed, for example, by selective wet etching.

One method for reducing TIR loss includes depositing on a growthsubstrate an n-type layer, an active layer, and a p-doped layer, forminga conductive substrate above the p-doped layer, removing the growthsubstrate to expose the n-doped layer, followed by photo-electrochemical(PEC) oxidation and etching of the n-doped layer to form a roughenedsurface to enhance the light extraction. A 2-fold increase in LED lightextraction has been achieved by this method compared to an LED with aflat, light emitting surface. One disadvantage of this method is that arandom distribution of roughness amplitude, up to 0.5 μm, can lead to anonuniform distribution of current over the surface due to thicknessnonuniformity in the n-type layer, which is often critical for thin-filmLEDs with the n-type layer thinner than 2-3 μm.

One method for manufacturing thin-film LEDs includes growing the firstand second epitaxial layers of different conductivity types with anactive layer between them on a growth substrate, providing a packagesubstrate with contact pads for the first and second epitaxial layers ofindividual LEDs, bonding the second epitaxial layer to the contact padsof the package substrate using a metal interface, removing the growthsubstrate, etching the exposed surface of the first epitaxial layer suchthat the LED layers have a thickness less than 10 μm or less than 3 μm,forming light extraction features in the primary emission surface toenhance the light extraction from an exposed light emitting surface ofthe first epitaxial layer which includes of roughening, patterning, anddimpling the primary emission surface, or forming a photonic crystal.The efficiency of a thin-film LED was enhanced both by surface featuresand by thinning the layers, removing the substrate absorbing the part ofthe light, making the reflecting contact at the side of the mountingsubstrate, and lowering the LED heating due to heat removal into themounting substrate. However, the creation of micron- and submicron-sizedroughness with a random profile is not consistent with the trend ofthinning LED layers down to a total LED thickness of less than 3 μm.

BRIEF SUMMARY

One embodiment is a light emitting diode having a plurality of layersincluding at least two layers. A first layer of the plurality of layershas a nanostructured surface which includes a quasi-periodic,anisotropic array of elongated ridge elements having a wave-orderedstructure pattern, each ridge element having a wavelike cross-sectionand oriented substantially in a first direction.

Another embodiment is a device including the light emitting diodedescribe above.

Yet another embodiment is a hard nanomask having a plurality ofelongated elements formed from an aluminum-containing semiconductormaterial, other than pure aluminum nitride, and disposed in aquasi-periodic, anisotropic array having a wave-ordered structurepattern and a wavelike cross-section. At least some of the elongatedelements having the following structure in cross-section: an innerregion of the aluminum-containing semiconductor material and a firstouter region containing aluminum nitride covering a first portion of theinner region.

A further embodiment is a method of making a light-emittingsemiconductor device. The method includes depositing a layer ofamorphous silicon on a surface of an aluminum-containing semiconductorlayer; irradiating a surface of the amorphous silicon with an obliquebeam of nitrogen ions to form a wave-ordered structure in the layer ofamorphous silicon; and further irradiating the surface of the amorphoussilicon with an oblique beam of nitrogen ions to transfer thewave-ordered structure to a surface of the aluminum-containingsemiconductor layer forming a nanomask. The nanomask includes aquasi-periodic, anisotropic array of elongated elements having awave-ordered structure pattern and a wave-like cross-section.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the present invention aredescribed with reference to the following drawings. In the drawings,like reference numerals refer to like parts throughout the variousfigures unless otherwise specified.

For a better understanding of the present invention, reference will bemade to the following Detailed Description, which is to be read inassociation with the accompanying drawings, wherein:

FIG. 1A is a scanning electron microscope (SEM) top view of a hardnanomask having a period of 73 nm and formed on a surface of aluminumgallium arsenide (AlGaAs) by a N₂ ⁺ ion beam with energy E=5 keV at anangle of bombardment θ=53° from surface normal, according to theinvention;

FIG. 1B is a perspective and cross-sectional view of one embodiment ofelongated elements of a hard nanomask, according to the invention;

FIG. 1C is a perspective and cross-sectional view of another embodimentof elongated elements of a hard nanomask with a wave break, according tothe invention;

FIG. 1D is a perspective and cross-sectional view of yet anotherembodiment of elongated elements of a hard nanomask with a joint betweentwo waves, according to the invention;

FIG. 1E is an SEM 70° angled view of a hard nanomask having a period of73 nm and formed on a surface of aluminum gallium arsenide (AlGaAs) by aN₂ ⁺ ion beam with energy E=5 keV at an angle of bombardment θ=53° fromsurface normal, according to the invention;

FIG. 2A is an SEM top view of a hard nanomask having a period of 73 nmand formed on a surface of AlGaAs by a N₂ ⁺ ion beam with energy E=5 keVat an angle of bombardment θ=53° from surface normal, which wassubjected to wet etching, according to the invention;

FIG. 2B is a perspective and cross-sectional view of one embodiment ofelongated elements of a hard nanomask which was subjected to wetetching, according to the invention;

FIG. 2C is an SEM 70° angled view of a hard nanomask having a period of73 nm and formed on a surface of AlGaAs by a N₂ ⁺ ion beam with energyE=5 keV at an angle of bombardment θ=53° from surface normal, which wassubjected to wet etching, according to the invention;

FIGS. 3A and 3B are corresponding SEM top views of nanostructuredsurfaces of silicon carbide (SiC) and sapphire (Al₂O₃) substrates with aperiod of quasi-periodic nanostructures of about 70 nm, according to theinvention;

FIGS. 4A to 4D each include several perspective and cross-sectionalviews of sequential transformations of hard nanomasks intonanostructured surfaces by different methods of nanostructuring LEDsurfaces and LED substrates, according to the invention:

FIG. 4A corresponds to the nanomask on a layer of amorphous silicon,according to the invention;

FIG. 4B corresponds to the nanomask on a layer of aluminum-containingsemiconductor, according to the invention;

FIG. 4C corresponds to an intermediate metal nanomask on a surface ofLED substrate, according to the invention;

FIG. 4D corresponds to an intermediate metal nanomask on a surface oftransparent inorganic layer on LED substrate, according to theinvention;

FIGS. 5A to 5F are cross-sectional views of different embodiments ofnanostructured surfaces, according to the invention;

FIGS. 6A to 6D are cross-sectional views of different LED embodimentswith nanostructured surfaces, according to the invention.

DETAILED DESCRIPTION

The invention relates to the field of semiconductor devices forconverting electrical energy into light energy, in particular, to thefield of solid state light emitting diodes (LEDs). The invention alsorelates to the technology of forming a nanostructure (type oftopography) on the light emitting surface of LEDs. In at least someembodiments, the nanostructuctured surface may increase light outputrelative to an LED with the same structure, but no nanostructuredsurface. In at least some embodiments, the nanostructured surface mayimprove the quality of epitaxial semiconductor layers grown for the LED.The invention also relates to the use of a wavelike silicon nitridenanomask, which is self-forming during the irradiation of the surface ofan amorphous silicon layer by a beam of nitrogen ions, as well as to theuse of a wavelike nanomask based on aluminum nitride, which isself-forming during the irradiation of the surface of an AlGaAs layer bya beam of nitrogen ions. The invention also relates to the use of awavelike nanomask based on aluminum nitride, which is formed during ionsputtering as a result of the transfer of a self-forming nanomasktopography from a layer of amorphous silicon into an underlayer of asemiconductor compound containing aluminum. As a result of subsequentreactive ion etching (ME) through the nanomask a dense quasi-periodicarray of nanoelements with equal, or substantially equal, heights can beformed on the surface of LED substrates or on the light emitting surfaceof a LED. The period of the array is controllably varied from, forexample, 20 to 150 nm or more, and the ratio of nanoelement height tothe array period is varied from, for example, 0.5 to 5 or more.

In general, a LED can be formed with a nanostructured surface.Preferably, the nanostructured surface is a light emitting surface. FIG.6A shows one embodiment of a thin-film LED having an n-type GaN or AlGaNepitaxial layer 2, and a p-type GaN or AlGaN epitaxial layer 72, betweenwhich an undoped active layer 73 with one or more quantum wells isdisposed. The layer 72 can be connected to a reflective silver-basedcontact metallization 71 through which the LED chip is bonded to aleadframe of an LED package. The light-emitting surface 75 of p-typelayer 2 is nanostructured with an array of nanoridges 24 that scatterslight and may increase the light output from the LED. Light raysemitting from emission region are shown by lines with arrows in FIGS. 6Ato 6D. The light-emitting surface 75 is connected to a contact layer oftransparent conductive oxide 76 or to a contact metallization 77. Itwill be recognized that other materials could be used for the layersillustrated in FIG. 6A.

FIG. 6B shows one embodiment of a LED device with a primarylight-emitting surface 85 on the back external side of the substrate 32of, for example, silicon carbide. This LED includes contacts 81 and 87between which a transparent conductive substrate 32 and a light emissionregion 82 are disposed. The emission region 82 includes semiconductorlayers of opposite conductivity type between which an active layer issandwiched that generates light when a voltage is applied to thecontacts 81 and 87 and current flows through the LED. The surface 85 onthe back external side of the LED substrate is nanostructured with anarray of elements 32 b that scatters the light and may increase thelight output from the LED.

FIG. 6C shows one embodiment of a LED device having a nanostructuredsurface 98 with an array of elements 32 a on the front internal side ofa substrate 32 (for example, a sapphire substrate). For example, the LEDincludes an n-GaN layer 91, an n-AlGaN layer 92, an undoped active layer93 with one or more quantum wells, a p-AlGaN layer 94, a p-GaN layer 95,and contact metallizations 96 and 97.

FIG. 6D shows an embodiment of an LED device that differs from thedevice shown in FIG. 6C in that the elements 52 a are made of atransparent inorganic material. Nanostructured surface 98 in FIGS. 6C to6D is designed to improve the quality of the epitaxial growth of n-GaNlayers 91 and, preferably, to enhance the light scattering by thesurface 98, which, preferably, allows increasing the internal quantumyield and light output from the n-GaN layer 91 into the substrate 32 andultimately increasing the LED's efficiency. It will be recognized thatany of the LED structures described above with respect to FIGS. 6A-6Dcan be made of using a variety of known semiconductor and other relatedmaterials.

Wave-ordered structures (nanomasks) can be formed on surfaces andsubstrates of LEDs by a broad ion beam. This equipment is produced, forexample, by German company Roth & Rau AG. The size of the ion beam issufficient for processing LED substrates of at least 50, 75, 100, and150 mm in diameter. In specific example, the ion energy is up to 2 keVand the current density is 1 mA/cm². For 150-mm LED wafers, theseparameters can provide the processing throughput of over 120 wafers perhour.

Methods of forming a nanomask on a silicon wafer are described in U.S.Pat. No. 7,768,018 and U.S. Patent Application Publication No.2008/0119034, both of which are incorporated herein by reference. Ultrathin membranes based on wave-ordered structure patterns are described inU.S. Pat. No. 7,604,690, which is incorporated herein by reference. Inat least some embodiments, a wavelike silicon nitride nanomask is formedby irradiation of the surface of a silicon wafer or silicon layer by abeam of nitrogen ions and then etching (e.g., wet etching or reactiveion etching) to create a nanostructured surface of the silicon in theform of a dense quasiperiodic array of nanoridges or nanopeaks. Thisnanomask can be used for fabricating LED devices from a wafer with ananostructured surface. In at least some embodiments, the average periodof the array is controllably varied in a range from 20 to 150 nm (or 20to 180 nm or 20 to 200 nm) to increase the performance of LED devices.This process is reliably reproducible and forms a uniform wavelikesilicon nitride nanomask, as well as a nanostructure on the surface ofsilicon.

A wavelike hard nanomask can also be formed by a beam of nitrogen ionsin layers of both amorphous silicon and aluminum-containingsemiconductor materials, other than pure aluminum nitride AIN, includingthose in the group that includes AlAs, AlGaAs, AlGaInP, AlGaN, andAlGaInN. The nanomask can be used for nanostructuring a LED lightemitting surface or a surface of a growth substrate for LEDs.Nanostructured surfaces can include one or more quasi-periodic arrays ofnanoelements having wave-ordered structure pattern and can be formed bymethods of selective etching, both wet and dry, including reactive ionetching (ME.) The period of the array is controllably varied from 20 to150 nm or more.

These methods and structures described herein can provide a reliablyreproducible and uniform wavelike nanomask for nanostructuring a LEDlight emitting surface or a surface of a growth substrate of up to 150mm or more in diameter for LEDs. A nanostructure having a wave-orderedstructure pattern on a LED light emitting surface or on a surface ofgrowth substrates for LEDs can be manufactured using broad ion beams andME plasma systems used in modern industry.

One embodiment is a hard nanomask having a plurality of elements as aquasi-periodic, anisotropic array of elongated elements having awave-ordered structure pattern and a wavelike cross-section. At leastsome of the elements have the following structure in cross-section: aninner region of aluminum-containing compound semiconductor, other thanpure aluminum nitride, and a first outer region containing aluminumnitride covering a first portion of the inner region and being formedfrom the aluminum-containing semiconductor material using a nitrogen ionbeam. In at least some embodiments, the first outer regions of theelements form a net-like or an island-like structure or a combinationthereof. In at least some embodiments, the period of the array is in arange from 20 to 150 nm or more. In at least some embodiments, thealuminum-containing semiconductor material is one of the following:AlAs, AlGaAs, AlGaInP, AlGaN, or AlGaInN.

In at least some embodiments, the nanomask also includes a second outerregion containing aluminum nitride being formed from analuminum-containing semiconductor material by a nitrogen ion beam,covering a second portion of the inner region, and connecting with thefirst outer region at a wave crest. The first outer region issubstantially thicker than the second outer region. In at least someembodiments, the nanomask includes AlGaAs as the aluminum-containingsemiconductor material and the processing method includes irradiatingAlGaAs surface using an oblique beam of nitrogen ions until the nanomaskis formed.

One embodiment is a method of forming a hard nanomask having awave-ordered structure pattern on a surface of an aluminum-containingsemiconductor, other than pure aluminum nitride. The method includesdepositing a layer of amorphous silicon on the surface of thesemiconductor, sputtering a surface of the amorphous silicon layer by anoblique beam of nitrogen ions until a wave-ordered structure is formedin the layer of amorphous silicon, further sputtering the amorphoussilicon layer by the oblique beam of nitrogen ions until the topographyof the wave-ordered structure is transferred on the surface of thesemiconductor and a hard nanomask is formed. The nanomask has aquasi-periodic, anisotropic array of elongated elements with awave-ordered nanostructure pattern and a wavelike cross-section. Atleast some of the elements have the following structure incross-section: an inner region of the compound, a first outer regioncontaining aluminum nitride covering a first portion of the innerregion, and a second outer region containing aluminum nitride covering asecond portion of the inner region and connecting with the first outerregion at a wave crest, where the first outer region is substantiallythicker than the second outer region and where aluminum nitride isformed from the compound by the nitrogen ion beam. In at least someembodiments, the first outer regions of the elements form a net-like oran island-like structure or a combination thereof. In at least someembodiments, the period of the array is in a range from 20 to 150 nm or20 to 200 nm. In at least some embodiments, the aluminum-containingsemiconductor is one from the group that includes AlAs, AlGaAs, AlGaInP,AlGaN, and AlGaInN.

In at least some embodiments, for a beam of nitrogen ions with N⁺ ionsand N₂ ⁺ ions in the relative fractions of x and (1−x), respectively,the nanomask average period, the nanomask formation depth, and the iondose to form the nanomask are (1+x) times greater than those for a N₂ ⁺ion beam.

In at least some embodiments, etching a hard nanomask is performed untilthe second outer regions of the elements are removed. In at least someembodiments, etching is performed as a wet etch in a liquid solution, ora dry etch in plasma, or an ion beam etch.

One embodiment is a light emitting diode including layers of materials,at least one of which has a surface where at least a portion of thesurface has a nanostructure having a quasi-periodic, anisotropic arrayof elongated elements along the surface, the elongated elements having awave-ordered structure pattern and being substantially equal incross-section shape and in height. In at least some embodiments, atleast some of the elongated elements form a net-like or an island-likestructure or a combination thereof. In at least some embodiments, theperiod of the quasi-periodic array is in a range from 20 to 150 nm or 20to 200 nm. In at least some embodiments, the elongated element height toarray period ratio is in the range from 0.5 to 5. In at least someembodiments, the surface is a light emitting surface of semiconductormaterial and the surface includes the nanostructure to enhance lightextraction. In at least some embodiments, the semiconductor material isone of the group that includes A₃B₅ compounds that include galliumphosphide (GaP) or gallium arsenide (GaAs), and III-N compounds thatinclude gallium nitride (GaN).

In at least some embodiments, the surface is a light emitting surface onthe back external side of the substrate and the surface includes thenanostructure to enhance light extraction. In at least some embodiments,the surface is a surface on the front internal side of the substrate, onwhich a layer of semiconductor material is disposed and which includesthe nanostructure to enhance light extraction and to improve the qualityof epitaxy of the semiconductor material. In at least some embodiments,the surface is a surface on the front internal side of the substrate andthe elongated elements are formed from a layer of transparent inorganicmaterial and disposed between the substrate and the layer ofsemiconductor material, and the substrate is connected withsemiconductor material between the elongated elements.

In at least some embodiments, the substrate is made of an inorganiccrystal, which is one of the group that includes sapphire (Al₂O₃),silicon (Si), silicon carbide (SiC), spinel (MgAl₂O₄), neodymium gallate(NdGaO₃), lithium gallate (LiGaO₂), zinc oxide (ZnO), magnesium oxide(MgO), A3B5 compounds that include gallium phosphide (GaP) or galliumarsenide (GaAs), and III-N compounds that include gallium nitride (GaN).In at least some embodiments, the substrate is made of an inorganiccrystal and the elements are substantially oriented in one directionwith respect to the substrate crystal.

One embodiment is a substrate for a light emitting diode, at least oneside of which has a surface, at least a portion of the surface having ananostructure including a quasi-periodic, anisotropic array of elongatedelements along the surface, the elongated elements having a wave-orderednanostructure pattern, and being substantially equal in cross-sectionshape and in height. In at least some embodiments, at least some of theelongated elements form a net-like or an island-like structure or acombination thereof. In at least some embodiments, the period of thequasi-periodic array is in a range from 20 to 150 nm or 20 to 200 nm. Inat least some embodiments, the elongated element height to array periodratio is in the range from 0.5 to 5. In at least some embodiments, theelongated elements are formed from a layer of transparent inorganicmaterial and disposed on the substrate surface, and the substrate isexposed between the elongated elements.

In at least some embodiments, the substrate is made of an inorganiccrystal, which is one of the group that includes sapphire (Al₂O₃),silicon (Si), silicon carbide (SiC), spinel (MgAl₂O₄), neodymium gallate(NdGaO₃), lithium gallate (LiGaO₂), zinc oxide (ZnO), magnesium oxide(MgO), A3B5 compounds that include gallium phosphide (GaP) or galliumarsenide (GaAs), and III-N compounds that include gallium nitride (GaN).In at least some embodiments, the elongated elements are substantiallyoriented in one direction with respect to the substrate crystal.

For a wavelike hard nanomask having a wave-ordered structure patternwith a period in the range from 20 to 150 nm or more and self-assembledon a silicon surface by an oblique beam of nitrogen ions, it has beenfound that an outer region of the nanomask element, which is irradiatedby the beam of nitrogen ions at an angle θ of, for example, about 70°with respect to its normal, is made of silicon nitride (SiN) if thenanomask is not exposed to air after its formation by the beam ofnitrogen ions in vacuum. After exposure to air, a small amount ofsilicon oxynitride inclusions is additionally produced in the outerregion. The thickness of the outer region may not be constant incross-section and can be smallest in the middle between its borders andincreasing in the direction of its edges.

In at least some embodiments, for nitrogen ions N₂ ⁺, the thickness ofthe first outer SiN region that is irradiated by nitrogen ion beam atangle θ of about 15° with respect to its normal is determined by theformula: T(nm)=2E(keV), where T is the thickness of the first outerregion, nm, and E is the energy of ions N₂ ⁺, keV. In at least someembodiments, for atomic nitrogen ions N⁺, the thickness of the firstouter region is two times greater than that for molecular ions N₂ ⁺. Insome embodiments, the nanomask period for the ions N⁺ is also two timeshigher than for the ions N₂ ⁺. A beam of N⁺ ions with energy E/2 and abeam of N₂ ⁺ ions with energy E form nanomasks with the same period andsame thicknesses of the first outer regions. For a beam of nitrogen ionshaving an x fraction of N⁺ ions and a (1−x) fraction of N₂ ⁺ ions, thenanomask period and the thickness of the first outer region have valuesthat are (1+x) times greater than those for a beam of N₂ ⁺ ions. Onefeature of the pattern of the wavelike hard nanomask of silicon nitrideon silicon is that the regions (opposite wave slopes) form anisland-like or a net-like structure or a combination thereof. Inaddition, the nanomask does not contain repetitive identical elementswith a length of at least not less than 5 periods of the array and doesnot contain repeating parts of the array with the same relativepositions of the elements, which is due to the self-forming nature ofthe nanomask.

In at least some embodiments, the phenomenon of self-forming generates ahard wavelike nanomask with controllable period in the range 20 to 150nm or more on the surface of AlGaAs, an aluminum-containingsemiconductor, formed by an oblique beam of nitrogen ions with energiesin the range of, for example, 0.5 to 8 keV. It was found in specificexamples that the wave slopes of the nanomask are ˜30° tilted withrespect to the nanomask plane; the first outer region of the nanomaskelement having been irradiated by a beam of nitrogen ions at an angle ofabout 15° with respect to its normal, like the second outer region ofthe nanomask element having been irradiated by a beam of nitrogen ionsat an angle of about 70° with respect to its normal, containsion-synthesized aluminum nitride (AlN). This nanomask is of highcontrast due to the significant difference in thickness between thefirst and second outer regions, which opens up the possibility of usingselective methods for its etching.

In at least some embodiments, under similar conditions of irradiation bynitrogen ions, the thickness of the first region containing AlN in thenanomask on Al_(0.2)Ga_(0.8)As is approximately 2 times smaller than thethickness of the first region of SiN in a nanomask formed on silicon.Also in the case of self-forming nanomask on AlGaAs, for a beam ofnitrogen ions having an x fraction of N⁺ ions and a (1−x) fraction of N₂⁺ ions, the nanomask period and the thickness of the first outer regionhave values that are (1+x) times greater than those for a beam of N₂ ⁺ions. One feature of the pattern of the wavelike hard nanomask on AlGaAsis that the regions form an island-like or a net-like structure or acombination thereof. In addition, the nanomask does not containrepeating parts of the array with the same relative positions of theelements, which is due to the self-forming nature of the nanomask. Itmay differ in higher ordering of the pattern compared to a self-formingnanomask on silicon.

In addition, it was found that the wavelike hard nanomask can be createdin a layer of aluminum-containing semiconductor from the group thatincludes AlAs, AlGaAs, AlGaInP, AlGaN, and AlGaInN through the transferof the topography of a self-forming wavelike nanomask from a layer ofamorphous silicon into the specified aluminum-containing layer during asputtering process with nitrogen ions. In this case the first and secondouter regions of the nanomask element contain ion-synthesized aluminumnitride (AlN). Depending on the ratio of N⁺ and N₂ ⁺ components in theion beam, the thickness of the first region of nanomask elements and itsperiod obey the regularity described above for the nanomask on AlGaAs.

FIG. 1A is a SEM image with enhanced contrast (without halftones, topview) of a self-forming wave-ordered structure (WOS) on the surface ofan aluminum gallium arsenide (AlGaAs) layer. This particular example isa wavelike hard nanomask 1 with an average period 3 (wavelength λ=73nm). The width of the SEM image is 2.5 μm. White stripes 10 and blackstripes 20 are the opposite slopes of the WOS waves.

FIG. 1B is a perspective view of a WOS region with a cross section ofwaves in the XZ plane on the surface of AlGaAs 2. The location of thewave slopes 10 and 20 and their orientation are the same as in FIG. 1A,corresponding to the XY plane. Wave crests are on average parallel tothe Y axis, i.e., the array of waves is anisotropic. A single wave(nanomask element) in the cross-section includes an inner region ofAlGaAs that further includes a first part 100 of the inner region and asecond part 200 of the inner region and an outer region that furtherincludes the first part 10 of the outer region containing aluminumnitride (AlN) and the second part 20 of the outer region also containingaluminum nitride. Regions 10 and 20 are formed from AlGaAs by a beam ofnitrogen ions N₂ ⁺ with energy in the range from, for example, 1 to 8keV in vacuum during nanomask formation and are connected to each otherat a wave crest or peak. In this particular example, the slopes of thewaves of nanomask 1 are about 30° tilted relative to the XY plane of thearray of waves.

As seen in FIG. 1A, waves of nanomask 1 have breaks, bends, andbranches, i.e. joints with each other. Generally the waves are elongatedalong the Y axis and elongated elements have length in the range from10λ to 30λ. At the same time there are waves having more or lesselongation as well as subwavelength pointlike elements with a size ofless than λ. In general, the array of waves is quasi-periodic and thepattern of waves is uniform, and one can reproduce these arrays with thesame average period in a range from 20 to 150 nm or more and the sameaverage elongation of waves under the same conditions of self-formation.However, repetitive waves with elongation of greater than 5λ andrepetitive parts of the array with the same relative positions of thewaves cannot generally be formed due to the self-forming nature of thenanomask.

A characteristic feature of the topology of nanomask 1 in FIG. 1A isthat the regions 10 of some elongated elements are connected to eachother, and regions 20 of some elongated elements are also connected in abranched structure or a mesh. At the same time there are both separatedregions 10 and separated regions 20.

In at least some embodiments, regions 10 in the XZ section plane at theborders have a beaklike shape. The thickness of region 20 in itscross-section in XZ plane may be smallest at the middle point 7 betweenthe regions 10 and gradually increase towards the regions 10.

The nanomask shown in FIGS. 1A to 1B can be formed on the AlGaAs surfaceby a beam of nitrogen ions N₂ ⁺. In one example, a nanomask can beformed with a beam of nitrogen ions N₂ ⁺ having energy of 5 keV anddirected in the XZ plane along the arrow 31 obliquely at an angle 0=53°from Z axis. The projection of the ion flow 31 on the XY plane is alongX axis. During sputtering of AlGaAs by nitrogen ions, a self-formingprocess occurs that results in the formation of wavelike nanomask 1 atthe sputtering depth D_(F)=130 nm from the initial level of AlGaAssurface. Regions 10 are bombarded by nitrogen ions at near normalangles, and regions 20 are bombarded at glancing angles of about 70° orlarger, which may determine, at least in part, the thickness of regions10 and 20. Crests of nanomask waves in an array are predominantlyoriented perpendicular to the projection of the N₂ ⁺ ion flow on thesurface of AlGaAs, i.e., perpendicular to the X axis. With decreasingion energy and increasing ion bombardment angle θ measured from surfacenormal (Z axis), the wavelength λ or period 3 of the array is reduced.As an example, in at least some embodiments ion energy in a range from 1to 8 keV corresponds to a range of nanomask period from 20 to 150 nm. Inat least some embodiments, the topology of nanomask 1 does not changefor the bombardment angles in the range θ=45°-55°.

FIG. 1C shows a wave break 19. End surfaces of the illustrated wavebreaks 19 were irradiated by a beam of nitrogen ions at grazing anglesof about 70° or greater; therefore they have the same thickness asregions 20 and connect regions 20 in a net-like structure.

FIG. 1D shows a wave joint 18. The surfaces of the illustrated joints ofwaves 18 were irradiated by a nitrogen ion beam at an angle of less than30°, therefore they have the same thickness as regions 10, and regions18 may connect regions 10 in a net-like structure. The thickness ofregions 18 is slightly smaller than the thickness of regions 10 locatedalong the Y axis.

FIG. 1E shows a SEM 70° angled view of a cleft hard nanomask on asurface of aluminum gallium arsenide (AlGaAs), which is shown in FIG.1A. The image width is 2.5 μm. It is seen in the cleft that the surfaceof AlGaAs is non-planar with the vertical size of roughness of 100 nmand the horizontal size of 2 μm. The wave shape in cross-section is seenas well.

FIG. 2A shows an SEM image with enhanced contrast (without halftones,top view) of a modified nanomask 9 with a quasi-periodic array ofcrest-like waves with regions 10 b on the surface (white stripes) spacedby trenches 23 (black stripes). In this example, the average period 3 ofthe array is 73 nm (wavelength λ=73 nm). The width of the SEM image is2.5 μm.

FIG. 2B shows a cross-section of crest-like waves (elongated elements)of a nanomask 9 in the XZ plane. The array elements are projections 8elongated along the Y axes and spaced by trenches 23. The projections 8include a lower region 2 of AlGaAs and an upper region 10 b containingaluminum nitride (AlN) that was formed from AlGaAs by a nitrogen ionbeam N₂ ⁺. Upper regions 10 b are disposed obliquely relative to the XYplane of the array.

FIG. 2C shows a SEM 70° angled view of a cleft of a hard nanomask 9.Nanomask 9 shown in FIGS. 2A to 2C is obtained from nanomask 1 as aresult of etching with removal of areas 20 and forming trenches 23 intheir places in AlGaAs 2. In this case, a wet selective etching ofAlGaAs with respect to AIN was implemented at room temperature in asolution containing H₂SO₄, H₂O₂, and water. In this isotropic etchant,the regions 10 of aluminum nitride are etched at a slower rate thanAlGaAs. Therefore, nanomask 9 differs from nanomask 1 by the absence ofregions 20 and by the presence of trenches 23 on their place. Due to theisotropy of the etching process, the ratio of the nanostructure heightto its period (aspect ratio) is limited by the value of ˜0.7 for thisetchant.

The formation of nanomask 9 can be implemented by other known methods,both wet and dry, for selectively etching aluminum-containingsemiconductors with respect to aluminum nitride such as, for example,reactive ion etching (RIE) in Cl₂/BCl₃/N₂ plasma. Depending on theetching mode, different cross-section shapes of elongated elements canbe formed. Using RIE, the aspect ratio values of the structure can bevaried in the range 1-5 due to the anisotropic nature of the etchingprocess while providing sufficient selectivity.

FIG. 3A shows a SEM top view of a quasi-periodic wavelike nanostructureon the surface of silicon carbide (SiC) with a period of about 70 nm,which was formed by transferring the topography of a wave orderedstructure from a layer of amorphous silicon onto the SiC surface throughsputtering by nitrogen ions. (For a general discussion of transferringthe topography, see, for example, Smirnov V. K., Kibalov D. S. Methodfor Shaping Nanotopography on a Film Surface, Russian Patent RU2204179,incorporated herein by reference.) This method includes depositing alayer of amorphous silicon onto a film, sputtering amorphous silicon bya flow of nitrogen ions until a wave-ordered nanostructure is formed inthe amorphous silicon layer, transferring a relief of the wave-orderednanostructure onto a surface of the film by further sputtering the layerof amorphous silicon and the film with nitrogen ions. In this case, amonocrystalline SiC substrate served as the film.

By the same method, a quasi-periodic wavelike nanostructure was formedon the surface of a monocrystalline sapphire substrate (FIG. 3B). Itshould be noted that the aspect ratio of nanostructures that are formedby transferring the topography of a wavelike nanostructure from theamorphous silicon layer into an underlayer material by ion sputtering isclose to the aspect ratio of initial wavelike nanostructure of 0.33.

Increasing the aspect ratio of nanostructures is possible by selectiveetching using wavelike nanostructures as a nanomask as shown, forexample, in FIGS. 4A to 4D. FIG. 4A illustrates steps of a method fornanostructuring the light-emitting surface of a layer 2 of LED materialusing a nanomask on the surface of an amorphous silicon layer. As afilm, the layer 2 of LED material has a surface which is to benanostructured to enhance light output of LEDs. A layer of amorphoussilicon 22 is deposited on the surface of the layer 2; the surface ofthe layer 22 is irradiated by a flow of nitrogen ions 31 until awave-ordered structure 21 is formed which has relatively thick elongatedregions 110 and relatively thin elongated regions 120. Regions 110 and120 are of silicon nitride and are formed from silicon by the beam ofnitrogen ions. A wave-ordered structure 21, which is a nanomask, isformed at a distance D from the surface of the layer 2 as shown in thestructure 300. The orientation of the nanomask elements (waves) in theXY plane is given by the direction of the ion flow 31 in the XZ plane.The direction of the projection of ion beam 31 onto the XY planecoincides with the direction of the X axis. Waves in the array areoriented along the Y axis perpendicular to the projection of the ionbeam 31 on the XY plane.

Regions 120 are then removed thus enhancing the contrast of the nanomask21. In at least one embodiment, this process takes about 2 seconds andallows one to significantly accelerate the etching of nanomask 1. It canbe carried out in, for example, a non-selective He/CHF₃ plasma or in aselective (with respect to silicon nitride) O₂/Cl₂ plasma. In the lattercase, the bias on the wafer that is etched is briefly risen, whichprovides a mode of ion sputtering of regions 120. As a result thestructure 400 is formed.

Silicon is then etched, for example, by RIE using a chlorine O₂/Cl₂plasma that is selective to nitride, resulting in the structures401-404. In this plasma, both silicon and LED materials, for example,GaAs and AlGaAs are etched with a selectivity of at least 10 withrespect to silicon nitride. Other known plasma mixtures, in whichsilicon and LED materials are etched selectively with respect to siliconnitride, may also be used. At the beginning of the etching of silicon22, in the structure 401, the walls of the resulting trenches betweenthe regions 110 of silicon nitride are etched vertically; then theetching process leads to a gradual reduction in the thickness and widthof the regions 110 of silicon nitride (they are gradually transformedinto the regions 110 a, 110 b and 110 c). Thus, the walls of the regions22 a of amorphous silicon become sloped, as shown in the structure 401.During further etching, a layer of material 2 starts being etched; thewidth of the regions 22 b of amorphous silicon becomes smaller, and thestructure 402 is formed. The flow of plasma ions that are reflected downfrom the trench walls causes sharpening of the trench bottoms and thestructure 403 is obtained with even more narrow regions 22 c. After thecomplete removal of nanomask, i.e. regions 110 c and 22 c, the structureshape tends to a triangular profile as in the structure 404 with aquasi-periodic array of nanoridges 24 of material 2 having a sawtoothcross-section. Array period 3 coincides with the period of nanomask 21.Height 25 of nanoridges 24 is typically the same for all nanoridges inthe array. The ratio of nanoridge height 25 to the array period 3 mayvary in the range from 1 to 3.

FIG. 4B illustrates steps of a method for nanostructuring alight-emitting surface of the layer 2 of LED material using a nanomaskon the surface of a layer of an aluminum-containing semiconductor. Inthis method, the structure 300 during further sputtering of the layer 22of amorphous silicon and the layer 2 of the LED material, for example,AlGaAs, by a flow of nitrogen ions 31 is transformed into the structure410 that is a hard nanomask 1. In this case, in contrast to the waveliketopography, the nanomask 1 is formed on the surface of thealuminum-containing semiconductor 2. The nanomask 1 includes elongatedregions 10 and 20 containing aluminum nitride (AlN) that is formed fromthe semiconductor 2 by a beam of nitrogen ions. Then this nanomask isetched using, for example, a wet etchant that is selective with respectto AlN. In the case of AlGaAs an example of a known etchant isH₂SO₄/H₂O₂/H₂O.

First, the regions 20 are removed, and the structure 411 is formed. AsAlGaAs is etched, regions 10 are also etched and decrease in size (10 a,10 b) but significantly slower than AlGaAs as shown in the structures412 and 413. SEM views of the structure 413 (nanomask 9) are also shownin FIGS. 2A and 2C. Due to the isotropic nature of the etching thetrenches between regions 10, 10 a, and 10 b may have a roundcross-section. After etching of regions 10 b, the structure 414 isobtained and includes an array of nanoridges 24 a with sharp tops. In atleast some embodiments, in the case of isotropic wet etching, the ratioof nanoridge height 25 to the array period 3 does not exceed 1.0.

It should be noted that the hard nanomask 1 can be formed not only bytransferring the topography of wave-ordered structure from a layer ofamorphous silicon into the underlayer of AlGaAs, but also directly inthe AlGaAs layer in the process of self-formation upon irradiation ofthis layer by a flow of nitrogen ions. However, in the latter case, thethickness of the AlGaAs layer should be increased by a depth of thestructure formation (˜200 nm). Upon transferring the topography of thewave-ordered structure from amorphous silicon layer, the wavelike hardnanomask 1 is formed almost immediately on the surface of AlGaAs layer,and in this case the thickness of this layer can be 200 nm less thanthat in the case of a self-forming nanomask in the AlGaAs layer. Thus,the formation of nanomask 1 in a layer of aluminum-containingsemiconductor through the transfer of wave-ordered structure topographyfrom the layer of amorphous silicon may be the most suitable forthin-film LEDs having thin layers of semiconductor compounds.

The etching selectivity of GaN, AlGaN, and AlGaInN with respect toaluminum nitride (AlN) and silicon nitride (SiN) for known etchants ismoderate and reaches 5-6. Therefore, it can be difficult to formhigh-aspect ratio structures on the surface of materials that are basedon gallium nitride using nanomasks with thin layers of AlN and SiN notexceeding 10-20 nm. A significant increase in selectivity to 15 andabove for etching materials based on gallium nitride is possible throughthe use of nickel masks. ME processes are known with etching selectivityfor sapphire and silicon carbide with respect to nickel, which exceeds 7and 50, respectively.

FIG. 4C illustrates steps of a method for nanostructuring the surface ofa material 32 through the use of an intermediate metal nanomask, forexample, Ni nanomask. The structure 310 differs from the structure 300in FIGS. 4A to 4B in that, instead of material layer 2, material layer32 and metal layer 42 are used. The process of forming a wavelike hardnanomask 21 in a layer of amorphous silicon 22 is the same as describedabove. The contrast of nanomask 21 can be enhanced in HNO₃/HF wetetchant due to dissolution of regions 120 with the resulting formationof the structure 420. The etching of amorphous silicon between theregions 110 of silicon nitride in Cl₂/O₂ plasma results in the formationof the structures 423 and 424. In an RIE process, regions 110 withreduction in their thickness and width are transformed to the regions110 a and 110 b. Simultaneously the regions 22 a and 22 b of amorphoussilicon are formed. The etching of the metal layer, which can beperformed by any known method including sputtering by argon ions oretching in a liquid selective etchant, results in the structure 425 withareas 42 a of metal nanomask. If desired, the regions 110 b of siliconnitride and the regions 22 b of amorphous silicon can be removed using,for example, SF₆ plasma with the formation of the structure 426.

Then the RIE process is applied to material 32 using a plasma selectiveto Ni. For example, the etching of SiC can be implemented in SF₆ plasmawherein SiC to Ni etch selectivity is greater than 50 (see, for example,Chabert P. Deep etching of silicon carbide for micromachiningapplications: Etch rates and etch mechanisms, J. Vac. Sci. Technol. B,Vol. 19, Issue 4, 2001, pp. 1339-1345, incorporated herein byreference). In a BCl₃/N₂/Ar plasma, GaN to Ni etch selectivity reaches15 (see, for example, Liann-Be Chang, Su-Sir Liu and Ming-Jer Jeng,Etching Selectivity and Surface Profile of GaN in the Ni, SiO₂ andPhotoresist Masks Using an Inductively Coupled Plasma, Jpn. J. Appl.Phys., Vol. 40, 2001, pp. 1242-1243, incorporated herein by reference).The etch selectivity of sapphire with respect to Ni exceeds 7 in anOxford Instruments Plasmalab System 100 ICP-RIE tool. As a result ofRIE, the structure 427 is formed with elements 42 b of Ni-nanomask andelements 32 a on the surface of material 32. Further etching leads tothe removal of elements 42 b of the metal mask and to the sharpening ofthe structure profile by the mechanism described above resulting in theformation of the structure 428. Depending on the selectivity and RIEmodes, the ratio of height 25 of the elements 32 b to the array period 3may be in the range from, for example, 0.5 to 5.

FIG. 4D shows steps of a method for nanostructuring a transparentinorganic layer through the use of an intermediate metal nanomask. Inthis case, the structure 320 differs from the structure 310 in that alayer of transparent oxide 52 is disposed between the layer 32 and themetal layer 42. After the removal of layers 120 in plasma, the structure430 is formed. The etching of amorphous silicon between the regions 110of silicon nitride in Cl₂/O₂ plasma results in the formation of thestructures 433 and 434. In an RIE process, regions 110 with reduction intheir thickness and width are transformed to the regions 110 a and 110b. Simultaneously the regions 22 a and 22 b of amorphous silicon areformed. The etching of the metal layer, which can be performed by anyknown method including sputtering by argon ions or etching in a liquidselective etchant, results in the structure 435 with areas 42 a of metalnanomask. If desired, the regions 110 b of silicon nitride and theregions 22 b of amorphous silicon can be removed using, for example, SF₆plasma with the formation of the structure 436. The etching of atransparent oxide layer 52 through the metal nanomask is carried out byknown methods, and the structure 437 is formed with elements 52 a of thetransparent oxide layer and elements 42 b of metal nanomask. Forexample, a layer of silicon oxide can be etched selectively in C₄F₈/Arplasma. The metal nanomask is removed and the structure 438 is formedwith elements 52 a of transparent oxide on the surface of material 32 ofa LED substrate. In this case, the ratio of the element height 25 to thearray period 3 may be less than 1.0.

FIG. 5A shows possible wavelike cross-sectional shape of nanoridges 24 bwith convex walls, and FIG. 5B shows a profile of nanoridges 24 c withconcave walls. FIG. 5C shows a possible cross-sectional shape ofelements 32 b disposed on the light-emitting surface of a LED substrateof material 32. FIG. 5D shows elements 32 a and FIG. 5E shows elements52 a of the transparent oxide material, which are oriented along the<1-100> direction on the surface of a monocrystalline substrate 32 forLEDs. FIG. 5F shows tooth-shaped elements 52 b of a transparent oxidematerial on the surface of the substrate 32. Flat areas 17 on thesurface of a monocrystalline substrate 32 are necessary for epitaxialgrowth of crystalline semiconductor layers of LEDs.

In the description above examples of structures and methods usingspecific materials have been illustrated. It will be understood thatsimilar structures can be formed, and methods used, based on othermaterials. In particular, other semiconductor materials can be used inplace of the semiconductor materials described above. For example,gallium-containing semiconductor materials may be used instead ofaluminum-containing semiconductor materials.

The above specification, examples and data provide a description of themanufacture and use of the composition of the invention. Since manyembodiments of the invention can be made without departing from thespirit and scope of the invention, the invention also resides in theclaims hereinafter appended.

1. A hard nanomask, comprising: a plurality of elongated elements formedfrom an aluminum-containing semiconductor material, other than purealuminum nitride, and disposed in a quasi-periodic, anisotropic arrayhaving a wave-ordered structure pattern and a wavelike cross-section, atleast some of the elongated elements having the following structure incross-section: an inner region of the aluminum-containing semiconductormaterial and a first outer region containing aluminum nitride covering afirst portion of the inner region.
 2. The nanomask of claim 1, furthercomprising a second outer region containing aluminum nitride covering asecond portion of the inner region, and connecting with the first outerregion at a wave crest, wherein the first outer region is substantiallythicker than the second outer region.
 3. The nanomask of claim 1,wherein the aluminum containing semiconductor material is selected fromAlAs, AlGaAs, AlGaInP, AlGaN, and AlGaInN.
 4. A method of making thehard nanomask of claim 1, the method comprising: depositing a layer ofamorphous silicon on a surface of the aluminum-containing semiconductorlayer; irradiating a surface of the amorphous silicon with an obliquebeam of nitrogen ions to form a wave-ordered structure in the layer ofamorphous silicon; and further irradiating the surface of the amorphoussilicon with an oblique beam of nitrogen ions to transfer thewave-ordered structure to a surface of the aluminum-containingsemiconductor layer forming the hard nanomask.
 5. The method of claim 4,wherein the first outer region of the hard nanomask covers a firstportion of the inner region and the nanomask further comprises a secondouter region containing aluminum nitride covering a second portion ofthe inner region and connecting with the first outer region at a wavecrest, wherein the first outer region is substantially thicker than thesecond outer region.
 6. The method of claim 5, further comprisingetching the nanomask to remove the second outer region.
 7. The method ofclaim 4, wherein the aluminum containing semiconductor is selected fromAlAs, AlGaAs, AlGaInP, AlGaN, and AlGaInN.
 8. A method of making adevice using the hard nanomask of claim 1, the method comprising:depositing a layer of amorphous silicon on a surface of thealuminum-containing semiconductor layer; irradiating a surface of theamorphous silicon with an oblique beam of nitrogen ions to form awave-ordered structure in the layer of amorphous silicon; and furtherirradiating the surface of the amorphous silicon with an oblique beam ofnitrogen ions to transfer the wave-ordered structure to a surface of thealuminum-containing semiconductor layer forming the hard nanomask. 9.The method of claim 8, wherein the device is a light emitting diode. 10.The method of claim 8, wherein the aluminum containing semiconductor isselected from AlAs, AlGaAs, AlGaInP, AlGaN, and AlGaInN.
 11. The methodof claim 8, wherein the first outer region of the hard nanomask covers afirst portion of the inner region and the nanomask further comprises asecond outer region containing aluminum nitride covering a secondportion of the inner region and connecting with the first outer regionat a wave crest, wherein the first outer region is substantially thickerthan the second outer region.
 12. The method of claim 11, furthercomprising etching the nanomask to remove the second outer region. 13.The method of claim 12, further comprising, after removing the secondouter region, etching the portion of the aluminum-containingsemiconductor layer that was below the second outer region to form ananostructured surface.
 14. The method of claim 13, wherein the deviceis a light emitting diode comprising a plurality of layers including atleast two layers, wherein a first layer of the plurality of layers isthe etched aluminum-containing semiconductor layer with thenanostructured surface, the nanostructured surface comprising aquasi-periodic, anisotropic array of elongated ridge elements having awave-ordered structure pattern, each ridge element having a wavelikecross-section and oriented substantially in a first direction.
 15. Themethod of claim 14, wherein the aluminum containing semiconductor isselected from AlAs, AlGaAs, AlGaInP, AlGaN, and AlGaInN.
 16. The methodof claim 13, wherein the nanostructured surface is a light emittingsurface.
 17. The method of claim 12, further comprising etching thenanomask to remove the first outer region and form a nanostructuredsurface.
 18. The method of claim 17, wherein the device is a lightemitting diode comprising a plurality of layers including at least twolayers, wherein a first layer of the plurality of layers is the etchedaluminum-containing semiconductor layer with the nanostructured surface,the nanostructured surface comprising a quasi-periodic, anisotropicarray of elongated ridge elements having a wave-ordered structurepattern, each ridge element having a wavelike cross-section and orientedsubstantially in a first direction.
 19. The method of claim 18, whereinthe aluminum containing semiconductor is selected from AlAs, AlGaAs,AlGaInP, AlGaN, and AlGaInN.
 20. The method of claim 17, wherein thenanostructured surface is a light emitting surface.